1. Field of the Invention
The invention relates to a recording liquid to be attached in a droplet state to an object for the purpose of recording on the object, to a liquid cartridge having this recording liquid accommodated therein, and to a liquid discharge device and a liquid discharge method of forming the recording liquid accommodated in this liquid cartridge in a droplet state and discharging it onto an object from a discharge nozzle.
2. Description of the Related Art
Examples of a liquid discharge device include a printer device of an inkjet system of discharging an ink of a recording liquid onto recording paper which is an object, thereby printing images or letters. This printer device of an inkjet system has such an advantage that it is easy to attain low running costs, miniaturization of device and colorization of images or letters.
Examples of the inkjet system of discharging an ink include a diffraction system, a cavity system, a thermojet system, a Bubble Jet (registered trademark) system, a thermal inkjet system, a slit jet system, and a spark jet system. In such an inkjet system, an ink is discharged from a discharge aperture, a so-called nozzle, of an ink discharge head for discharging an ink in a state of a fine droplet and impacted on recording paper, thereby printing images or letters.
In the printer device of an inkjet recording system, there may be the case where the printing is carried out on not only dedicated papers for inkjet recording but also plain papers such as copying paper and writing pad. For that reason, an ink used in the inkjet recording system is required such that even in case where the printing is carried out on not only dedicated papers for inkjet recording but also plain papers, it is possible to achieve printing high-grade images or letters which are especially high in image density, free from bleeding of images or letters, concretely bleeding of boundaries between different colors and unevenness of mixed color, etc. and less in strike through of ink. In order to meet these requirements, examples of the ink which is used for the inkjet recording system include ones described in JP-B-60-23793 (Patent Document 1), JP-A-56-57862 (Patent Document 2), JP-A-6-157959 (Patent Document 3), JP-A-2003-3100 (Patent Document 4), JP-A-2003-253167 (Patent Document 5) and JP-A-8-170041 (Patent Document 6).
Patent Document 1 describes that by using a dialkyl sulfosuccinic acid as a surfactant, dryness is improved. However, according to the ink described in this Patent Document 1, not only a pH region of paper where it is expected to improve the dryness is narrow, but also an improving effect with a lapse of time is deteriorated or a print density is low.
Patent Document 2 describes that by adding a strongly basic substance in an ink, bleeding of an image is suppressed. However, according to the ink described in this Patent Document 2, the effect is useful for only acidic papers but is hardly revealed in plain papers of a neutral paper type.
Patent Documents 3 and 4 describe that by containing a specified amount of each of a wetting agent, a surfactant and 2-ethyl-1,3-hexaediol in an ink, image bleeding, especially image bleeding in a superposed color part is improved. However, according to the inks described in these Patent Documents 3 and 4, though the image bleeding can be improved, strike through of the image is large, the image density is low, and a sufficiently satisfactory high-grade image is hardly obtainable.
Patent Document 5 describes that by containing 2,4-diethyl-1,5-pentanediol in an ink, strike through of the ink is suppressed. However, according to the ink described in Patent Document 5, though image bleeding can be improved, likewise the foregoing Patent Documents 3 and 4, strike through of the image is large, the image density is low, and a sufficiently satisfactory high-grade image is hardly obtainable.
Patent Document 6 describes that by containing propylene glycol monopropyl ether, dryness and image bleeding are improved. However, according to the ink described in Patent Document 6, the effects on dryness and image bleeding are low, and a sufficiently satisfactory high-grade image is hardly obtainable, too.
In the printer device of an inkjet recording system, for example, a printer device capable of performing high-speed printing on recording paper, namely a line type printer device in which a range substantially the same as a width of recording paper is the discharge range of the ink, bleeding of images or letters, strike through of an ink and so on are remarkably caused (see, for example, JP-A-2002-36522 (Patent Document 7)).
In the line type printer device, an ink is discharged for every nozzle line in which nozzles for discharging an ink are arranged in parallel in a range substantially the same as the width of recording paper, thereby performing once printing in one line over the width direction of recording paper. Thus, a discharge cycle of the ink in every nozzle line is extremely short. For that reason, in the line type printer device, when permeation of an ink which is discharged one after the other into the recording paper is slow, bleeding of the ink on images or letters or the like is caused.
Then, in the line type printer device, it is necessary to use an ink having excellent penetration properties into recording paper.
However, in the line type printer device, in the case where printing is carried out on plain paper or the like by using an ink having excellent penetration properties, there may be a possibility that the print density becomes low because the ink excessively permeates in a depth direction, namely a thickness direction of the plain paper.
In the line type printer device, when so-called color printing in which inks having a different color from each other are discharged onto recording paper to achieve printing is carried out, even by using an ink having excellent penetration properties, since the discharge cycle of the ink in every nozzle line is extremely short, before the ink impacted on the recording paper sufficiently permeates into the paper, an ink of a next color is impacted one after the other. For that reason, in the line type printer device, there may be a possibility that bleeding of boundaries between the respective colors or unevenness of mixed color is caused.